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Residual Effects of Calcium Silicate in Tropical Soils: II. Biological Extraction of Residual Soil Silicon¹

ABSTRACT

A modified Neubauer seedling method utilizing rice (Oryza sativa, L.) as a test plant, was employed to study the bioavailability of residual Si in a Hawaiian Gibbsihumox soil. Adsorbed soil Si was also removed with 0.1N acetic acid adjusted to pH 3.5 and containing 50 ppm P (phosphate solution). The results show that more Si was extracted by plant and ratoon crops of rice combined than by phosphate solution because of longer extraction time during plant growth and also because of possibly greater efficiency of Si removal by rice roots. Rice seedlings extracted proportionately more native Si than did phosphate solution, which resulted in comparable amounts of applied Si being recovered by the two methods, i.e., 8 to 30% for rice and 13 to 23% for phosphate extraction. The results of this study show that 55 to 72% Si applied 5 years ago was still adsorbed by or precipitated in the soil in a form that these techniques could not measure. However, the findings of this study strongly indicate that the modified Neubauer technique can be efficiently employed to estimate the pool of potentially available soil Si in the highly weathered soils of the tropics.

¹ Contribution from Hawaii Agric. Exp. Stn., Univ. of Hawaii. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree in Agronomy and Soil Sci.

² Former Graduate Student, and Soil Scientist, respectively, Dep. of Agronomy and Soil Sci., Univ. of Hawaii, Honolulu, Hawaii, 96822. The senior author is now Assistant Professor, Center for Wetland Resources, Louisiana State Univ., Baton Rouge, LA 70803.

Received for publication May 16, 1977. Accepted for publication September 23, 1977.